1. Field of the Invention
This invention relates to a novel protease which has been isolated from a bacterial symbiont of the marine shipworm. The protease is uniquely characterized by stability over a broad pH range as well as tolerance to a variety of chemical environments. These properties render the protease useful in detergents and other low temperature industrial applications.
2. Description of the Prior Art
Proteolytic enzymes are conventionally used in detergent compositions, particularly in laundry detergents. One such enzyme commonly used is subtilisin. This enzyme is produced by Bacillus subtilis and is an effective stain removing agent. Proteolytic enzymes derived from a variety of other Bacillus species have been disclosed by Aunstrup et al. in U.S. Pat. No. 3,723,250. The sources of those species were largely soil samples and manures, and the enzymes were selected for optimal proteolytic activity against hemoglobin at pH above about 9.
Hora (Canadian Patent 1,247,025) recognizes the enzyme stability problems in enzymatic laundry detergents containing peroxide progenitors. Peroxy-type bleaching agents of concern are alkali metal persulphates, perphosphates, perborates, as well as alkali metal and alkaline earth metal salts of organic peracids. Hora discovered that the storage stability of these compositions could be improved by the inclusion of an alkali metal metaborate.
Another factor affecting the stability of proteolytic enzymes is pH. In U.S. Pat. No. 3,840,433, Aunstrup et al. identify a group of proteases produced by the cultivation of Bacillus alcalophilus. These enzymes are useful in the dehairing of hides, and can withstand the highly alkaline pH of a saturated lime solution or of a soda ash solution. Aunstrup et al. contend that the B. alcalophilus proteases exhibit maximum activity against hemoglobin at pH 12 and 25.degree. C. and also at pH 10.1 and 60.degree. C.
Hellgren et al. (U.S. Pat. Nos. 4,801,451 and 4,963,491) teach enzyme preparations from animals of the order Euphausiaceae as being useful in cleaning compositions for degrading and removing contaminants of biological origin. At optimum temperatures of 30.degree.-55.degree. C., these preparations display proteolytic activity in the pH range 5-10.
In U.S. Pat. No. 4,865,983, Durham et al. teach the use of proteases from Vibrio species in cleaning compositions, including laundry detergents, automatic dishwasher detergents, laundry bleaches and presoaks. These proteases are characterized by a high proteolytic activity, stability over wide pH and temperature ranges, and stability to oxidizing agents, including chlorine bleaches.
Lad et al. (U.S. Pat. No. 4,749,511) relate to contact lens cleaning solutions which are comprised of general-purpose proteases in combination with the endoproteinase lys-C for removing lysozyme from lens surfaces. The function of the endopeptidase is to specifically cleave at the carboxyl side of lysine residues and expose susceptible peptide bonds of lysozyme to the protease without concomitant inactivation of the protease. The cleaning solutions of Lad et al. include additional components which aid in the overall lysozyme degradation and solution stability.
In general, enzymes ideal for use in detergents and other cleansing compositions should possess a high level of activity on proteinaceous contaminants over a broad pH range and over a broad temperature range. They should also be stable in the presence of oxidizing agents, bleaches, surfactants and other additives commonly used in detergents. Some detergent applications present less stringent conditions than others and do not require enzymes having the optimum range of tolerances. For example, enzymes for room temperature presoaks and contact lens solutions typically do not require the same temperature stability range as all-temperature laundry detergents. Nonetheless, the search continues to extend the conditions of activity and stability of proteolytic enzymes for all applications.